title: Understanding verbal fluency in healthy aging, Alzheimer's disease, and Parkinson's disease.
abstract: OBJECTIVE
  Verbal fluency measures are frequently part of batteries designed to assess executive function (EF), but are also used to assess semantic processing ability or word knowledge. The goal of the present study was to identify the cognitive components underlying fluency performance.
  
  
  METHODS
  Healthy young and older adults, adults with Parkinson's disease, and adults with Alzheimer's disease performed letter, category, and action fluency tests. Performance was assessed in terms of number of items generated, clustering, and the time course of output. A series of neuropsychological assessments were also administered to index verbal ability, working memory, EF, and processing speed as correlates of fluency performance.
  
  
  RESULTS
  Findings indicated that regardless of the particular performance measure, young adults performed the best and adults with Alzheimer's disease performed most poorly, with healthy older adults and adults with Parkinson's disease performing at intermediate levels. The exception was the action fluency task, where adults with Parkinson's disease performed most poorly. The time course of fluency performance was characterized in terms of slope and intercept parameters and related to neuropsychological constructs. Speed of processing was found to be the best predictor of performance, rather than the efficiency of EF or semantic knowledge.
  
  
  CONCLUSIONS
  Together, these findings demonstrate that the pattern of fluency performance looks generally the same regardless of how performance is measured. In addition, the primary role of processing speed in performance suggests that the use of fluency tasks as measures of EF or verbal ability warrants reexamination.
authors.affiliation: Landon Center on Aging, University of Kansas Medical Center, Kansas City, MO, USA. mcdowdj@umkc.edu
authors.forename: Joan
authors.initials: J
authors.lastname: McDowd
authors.forename: Lesa
authors.initials: L
authors.lastname: Hoffman
authors.forename: Ellen
authors.initials: E
authors.lastname: Rozek
authors.forename: Kelly E
authors.initials: KE
authors.lastname: Lyons
authors.forename: Rajesh
authors.initials: R
authors.lastname: Pahwa
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Burns
authors.forename: Susan
authors.initials: S
authors.lastname: Kemper
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000544:Alzheimer Disease / Q000150:complications*; D000704:Analysis of Variance; D003072:Cognition Disorders / Q000175:diagnosis / Q000209:etiology*; D032882:Comprehension; D005260:Female; D006801:Humans; D007266:Inhibition, Psychological; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology; D008875:Middle Aged; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000150:complications*; D012660:Semantics; D013997:Time Factors; D014705:Verbal Behavior / Q000502:physiology*; D014706:Verbal Learning; D055815:Young Adult